"Invalid file" when trying to upload pics from my computer

[Corvette Kid]

Trying to add pics from my files into a post without success. I've done it many times over the years using "manage attachments"
in reply. But the last two or three times I've tried it doesn't work anymore. I don't know if it's a computer or forum problem, any ideas?
Thanks.

[J T]

What's the file extension? How large is the file? Could you upload the file to another provider so that one of us can examine it?